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Delegates celebrate after formally nominating former Secretary of State Hillary Clinton for president on the second day of the Democratic National Convention at the Wells Fargo Center, July 26, 2016, in Philadelphia.

The Democratic National Convention's lineup of speakers has highlighted an increasingly diverse country that could soon elect the first female president to succeed its first black chief executive.

Yet the stream of women, African-Americans, Latinos, gay Americans — from U.S. senators and celebrities to activists and, on Thursday, Democratic nominee Hillary Clinton herself — also serves as a reminder of Democrats' struggles to connect with most heterosexual white men.

Vice President Joe Biden confronted the reality Wednesday, telling delegates in Philadelphia that Trump's claims of being a middle-class savior are "malarkey" and that the Republican presidential nominee and billionaire real estate mogul "doesn't have a clue about the middle class." Earlier in the day, Biden told MSNBC that Democrats have "done the right thing" for white working-class voters, but still haven't "spoken to them."

Chelsea Clinton Speaks at DNC

Chelsea Clinton Speaks at the Democratic National Convention on Thursday night.

(Published Friday, July 29, 2016)

It's a long-developing gap that bolsters Republican control of Congress and most statehouses. It could play into the hands of Republican Trump, whose path to victory depends on whites drawn to his blistering critiques of elitism and "political correctness" in the America of Clinton and Barack Obama.

White men still make up about a third of the typical presidential electorate and will be crucial to Trump's fortunes in Rust Belt states that have seen a declining middle class. They also could tip the balance in battlegrounds like Virginia and Florida, states Obama won twice.

Saunders says both parties play "wedge and identity politics" on many issues. Republicans emphasized "law and order" at their Cleveland convention, while Democrats on Tuesday welcomed "Mothers of the Movement," black moms whose sons died at the hands of police. Republicans heard National Rifle Association leaders; Democrats are featuring families of gun violence victims.

Democratic pollster Mark Mellman described "a cultural gap," with both parties playing to their advantages. But Saunders says Trump taps into a "legitimate" frustration acute among small-town and rural white men whose fathers and grandfathers once helped elect Democrats.

"They see no opportunity, no hope," continued Saunders, who advised John Edwards' presidential campaigns and Jim Webb's brief 2016 bid. "Then they see Democrats up there talking about diversity and trends and what we'll be like in 40 years. This country needs help now."

Democrats insist they understand the sentiment.

Hillary Clinton Quotes Roosevelt's Fear Speech

Remarking on Donald Trump's reliance on fear, Hillary Clinton quoted President Franklin Delano Roosevelt's famous fear quote that he gave during the throes of the Great Depression.

(Published Friday, July 29, 2016)

Former President Bill Clinton, speaking Tuesday on his wife's behalf, told of campaigning this year in West Virginia — a now heavily Republican state the former president won twice — in front of coal miners who blame job losses on Democrats' policies. "If she wins, she is coming back for you to take you along on the ride to America's future," Clinton recalled telling voters.

The white Pittsburgh police chief, Cameron McLay, told Democratic delegates that police and their communities can work together. The top organized labor leader, Richard Trumka, who is white, made the traditional appeal that Democrats are the party of workers.

Democrats' vice presidential nominee Tim Kaine, who is white, pitched his middle-class values Wednesday, touting his upbringing in Kansas City, the importance of his family and the influence of his faith, which he called his "north star for orienting my life." Clinton aides have touted Kaine's standing across Virginia, including some conservative, rural pockets.

Robby Mook, Clinton's campaign manager, said Wednesday that Clinton will address working-class issues in her nomination acceptance, as well.

In 2012, exit polls showed Republican Mitt Romney won 62 percent of white men to Obama's 35 percent. Measured another way, white men made up less than quarter of Obama's national vote, compared to about 44 percent of Romney's total.

Current polls suggest a more pronounced gap this year, a trends evident on the ground.

Clinton on Trump: 'A Man You Can Bait With a Tweet'

In her remarks at the DNC on July 28,2016, Hillary Clinton called her opponent Donald Trump "a man you can bait with a tweet" and "not a man we can trust with nuclear weapons."

(Published Friday, July 29, 2016)

In St. Clairsville, Ohio, not far from where both Clintons campaigned this spring, barber shop owner Kent Jenewein estimated that "more than 90 percent" of his clients, nearly all white men, back Trump — in a county Obama won in 2008. Clinton, Jenewein said, "doesn't understand us."

Mellman, the pollster, says Democrats can make "marginal gains" among non-urban whites, including men, in the same way Republicans are seeking marginal upticks in support from African-Americans and Latinos. Trump could also drive up his support among white men only to see Clinton buoyed with better support than Obama had from white Republican women who dislike Trump.

Clinton insisted during the primaries that she won't overlook white men. "Let's be honest," she said in her own Appalachia campaign stop. "Some (of you) find it hard to think about voting for any Democrats. ... But I'm going to keep trying to convince people otherwise."